The invention is directed to a micromechanical electrostatic relay having a base substrate that carries a base electrode layer and a base contact piece, and having an armature substrate that lies on the base substrate and has an armature spring tongue that is worked free and attached at one side and that carries an armature electrode layer and an armature contact piece at its free end. The spring tongue carries at least one layer that generates a mechanical stress relative to its substrate material such that the spring tongue is bent away from the base substrate by a steady curvature in the quiescent condition and conforms to the base substrate in the working condition when a voltage is present between the electrode layers, whereby the two contact pieces lie against one another
DE 42 05 029 C1 already discloses such a micromechanical relay. As set forth therein, such a relay structure can be manufactured, for example, of a crystalline semiconductor substrate, preferably silicon, whereby the spring tongue serving as an armature is worked out of the semiconductor substrate by appropriate doping and etching processes. By applying a control voltage between the armature electrode of the spring tongue and the planar base electrode, the curved spring tongue rolls on the base electrode and thus forms what is referred to as a migrating wedge. The spring tongue is stretched during this rolling until the free end with the armature contact piece touches the base contact piece on the base substrate.
It is likewise already mentioned in general form in the above-recited publication that stresses can be generated in the spring tongue by specific, additional layers such as SiO.sub.2 and Si.sub.3 N.sub.4, the desired curvature in the quiescent condition being thereby achieved. This preferably occurs in that a layer that produces a compressive strain relative to the substrate material is applied on that side of the spring tongue facing toward the base electrode, the spring tongue uniformly curving away from the base substrate as a result thereof.
The coating with a stress-generating material, however, results in the fact that the stress forces act not only in one direction but toward all sides, so that the spring tongue is given not only the desired curvature in the longitudinal direction, but is also usually given an undesirable arc in the transverse direction. Given a spring tongue that carries the contact piece in the middle region of its free end, this means that the tabs of the spring tongue situated at both sides of the contact piece arc further upward away from the base substrate than the contact region. Without enlarging the contact spacing, the working air gap between the electrodes is thus enlarged in this region, the response voltage consequently also undesirably rising.